This invention relates to an exhaust gas heat exchanger system, and more specifically, to such a system intended for use with an internal combustion engine.
Emission concerns associated with the operation of internal combustion engines, generally, but not always, diesel engines, have resulted in an increased emphasis on the use of exhaust gas heat exchange systems with such engines, particularly, but not always, in vehicular applications. These systems are employed as part of an exhaust gas recirculation (EGR) system by which a portion of an engine""s exhaust is returned to its combustion chambers via its intake system. The result is that some of the oxygen that would ordinarily be inducted into the engine as part of its fresh combustion air charge is displaced with inert gases thus reducing the rate of NOx formation. EGR is also frequently designed to absorb heat from the combustion process, thus lowering its temperature and providing a further reduction in NOx. It has been shown that EGR is a very effective method in achieving NOx reduction.
As generally alluded to previously, dilution of the combustion air with inert gases decreases the oxygen concentration of the mixture being combusted with the engine, thereby reducing the availability of oxygen for combination with nitrogen that would result in NOx. Temperature reduction in the combustion process, also leading to a reduction in NOx, is believed to be primarily due to the heat absorbing capacity of CO2 and H2O in the exhaust gas and the disassociation of CO2 which reduces combustion pressures and temperatures.
In many applications employing EGR, exhaust gas heat exchangers are employed. In the usual case, engine coolant is brought into heat exchange relation with the exhaust gas prior to its recirculation so as to lower its temperature. Not only does this provide a beneficial effect in terms of a reduced temperature of the gases entering the combustion chamber, leading to reduced combustion temperatures and the associated reduction of NOx, it causes the exhaust gases to become more dense due to their reduction in temperature so that for a given volumetric recirculation flow rate, a greater quantity of the exhaust gas is recirculated to the intake side of the engine, thereby promoting greater dilution of the intake air and promoting the associated reduction in NOx.
However, there are instances during the cycle of operation of an internal combustion engine wherein reduction of the temperature of the exhaust gas by an exhaust gas heat exchanger is undesirable. For example, where the exhaust system for the internal combustion engine is equipped with a catalytic converter to treat exhaust gases to reduce emissions, it is generally necessary that the catalytic converter operate at a high temperature to be effective. Of course, at start up, the catalytic converter will be at ambient temperature and ineffective. Thus, at start up, it is desired that uncooled exhaust gas be discharged into the catalytic converter to quickly bring it up to a temperature whereat it may be effective. Moreover, some sources have indicated a preference for bypassing the exhaust gas heat exchanger in conditions such as idle or no load conditions which often improves idle, no load and part load fuel economy while reducing hydrocarbon and carbon monoxide emissions.
In some situations, it is difficult to achieve effective EGR because of the absence of a sufficient pressure differential between the exhaust gas recirculation line and the intake manifold. Thus, it is desirable that the exhaust gas heat exchange system minimize pressure drop so as to allow sufficient introduction of exhaust gases into the intake side of the engine to achieve the benefits of EGR.
The present invention is directed to overcoming one or more of the above problems.
It is the principal object of the invention to provide a new and improved exhaust gas heat exchanger for use with an internal combustion engine. Even more particularly, it is an object of the invention to provide such a system that is ideally suited for use with an internal combustion engine employed to propel a vehicle.
An exemplary embodiment of the invention achieves the foregoing objects in an exhaust gas heat exchange system for internal combustion engines which includes an intake manifold having an inlet for recirculating exhaust gas. Also included is an exhaust manifold having at least one inlet receiving exhaust gas from an engine as well as an outlet for discharging exhaust gas and spaced from the inlet(s). An exhaust gas heat exchanger includes a first flow path having an inlet connected to the exhaust manifold to receive exhaust gas therefrom, an outlet for discharging cooled exhaust gas and a second flow path in heat exchange relation with the first flow pass for receipt of a coolant whereby exhaust gas flowing in the first flow path may be cooled. An exhaust valve having a first inlet is connected to the first flow path outlet. It also includes a second inlet connected to the exhaust manifold and an outlet connected to the intake manifold inlet. A valve mechanism is included and has at least one movable component which is movable between positions (a) connecting the exhaust valve first inlet to the exhaust valve outlet and (b) connecting the exhaust valve second inlet to the exhaust valve outlet. Finally, an actuator is connected to the valve mechanism for moving the valve mechanism component(s) between the two aforementioned positions.
In one embodiment, the exhaust valve second inlet is connected to the exhaust manifold at a location downstream of the exhaust manifold inlet(s) and upstream of the exhaust manifold outlet.
A preferred embodiment contemplates that the exhaust valve second inlet be connected to the exhaust manifold closely adjacent to the exhaust manifold outlet.
In one embodiment, the first flow path inlet and the exhaust valve first and second inlets are approximately aligned with one another.
Preferably, the exhaust gas heat exchanger and the exhaust valve are mounted on the exhaust manifold.
In a highly preferred embodiment, the exhaust manifold is elongated and the second inlet is connected to the exhaust manifold at a location that is spaced from the exhaust manifold outlet a distance equal to one-half or less of the length of the exhaust manifold. Even more preferably, the distance is one-third or less of the length of the exhaust manifold.
A preferred embodiment of the invention contemplates that the exhaust manifold be elongated and the exhaust manifold outlet be adjacent to one end thereof. The exhaust gas heat exchanger first flow path inlet has a connection to the exhaust manifold at a location intermediate the ends thereof.
Preferably, the connection is closely adjacent and end of the exhaust manifold opposite the one end.
A preferred embodiment of the invention also contemplates that the exhaust gas heat exchanger and the exhaust manifold both be elongated and that the exhaust valve is mounted on one end of the exhaust gas heat exchanger to form an elongated assembly. The assembly is disposed generally parallel to the exhaust manifold.
In a highly preferred embodiment, the exhaust valve first inlet, second inlet and outlet intersect at a common location and the valve component(s) includes a valve member located at the common location.
Even more preferably, the exhaust gas heat exchanger is elongated and has an axis of elongation, and the exhaust valve first and second inlets are approximately aligned on the axis of elongation. The exhaust valve outlet is disposed approximately transverse to the axis of elongation.
Other objects and advantages will become apparent from the following specification taken in connection with the accompanying drawings.